Understanding the early predictors of autism is essential to promoting earlier identification, diagnosis and treatment. Although aberrant visual attention is one of the earliest identified predictors of autism and may play an integral role in the socio-communicative deficits inherent in the disorder, the emergence of atypical attention in infancy is poorly understood. The present proposal seeks to characterize the development of aberrant attention in autism by integrating cognitive and developmental neuroscience methods within a multiple-group, prospective longitudinal design. Methods will include computerized attention orienting and visual preference paradigms integrated with concurrently-measured heart-defined sustained attention. Integrating behavioral and heart-defined measures will critically inform whether behavioral eye movement reflects underlying cognitive processes of stimulus response. Patterns of behavioral and biomarkers will be compared across high risk infant siblings of children with autism (ASIBS), high risk infants with fragile X syndrome (FXS), and low risk controls; thus informing the etiological specificity of early attention indicators, which is essential to informing early diagnostic and treatment efforts. Specifically, we aim to: (1) evaluate group differences in attention orienting (disengagement, facilitation) and visual preference (social/nonsocial, novel/familiar) between 6, 9, and 12 months of age (9 and 12 months in FXS), (2) compare behavioral performance on computerized attention paradigms to heart-defined sustained attention, and (3) evaluate the relationship between autistic outcomes at 24 months and these early behavioral and biomarkers of attention. Multilevel modeling will be used to analyze the patterns of attention across high risk groups, as well as the relationship between early attention and autistic outcomes. This study is innovative in that it is the first to apply concurrently-measured behavioral and heart-defined attention to the prospective surveillance of infant attention in autism, as well as to compare behavioral and biomarkers of attention across high risk ASIBS and infants with FXS.